comparison of thermoluminescent charavteristics of lif and topaz tld's

Comparison of Thermoluminescent characteristics of LIF and Topaz made TLDs and their applicability to clinical radiotherapy: 

Comparison of Thermoluminescent characteristics of LIF and Topaz made TLDs and their applicability to clinical radiotherapy Mujeeb Ur Rahman MS Medical Physics PIEAS

Outlines: 

Outlines Introduction Thermoluminescence TL Characteristics Materials with TL Characteristics TL material as Radiation Dosimeter Properties desired for a TL Dosimeter Examples of TL Dosimeters Topaz as TLD Motivation Aims and Objectives Materials and Methods Sample Collection Sample Preparation Experimental Procedures Results and Discussion Conclusion and Future Recommendations References 3/28/2011 2

Introduction: 

Introduction [1]. C. Furetta , “Handbook of Thermoluminescence”, 2 nd Ed., World Scientific Publishing Co. Inc., USA, (2003) Thermoluminescence [1] The thermally stimulated emission of light from an insulator or semiconductor following the previous absorption of energy from Radiation Three Essential Ingredients Material must be an insulator or a semiconductor Material must have absorbed energy during exposure to ionizing radiation The luminescence emission is triggered by heating the material 8/8/2011 3

Thermoluminesence (cont.): 

Thermoluminesence (cont.) 8/8/2011 4 Valance Band Emission Conduction band Valance Band Conduction band Valance Band Conduction band RC RC RC T T T Excitation Heating Heating [2]. A. J. J. Bos , “Theory of thermoluminescence”, Radiation Measurements, vol. 41, pp- S45–S56, 2007

TL Characteristics (cont.): 

TL Characteristics (cont.) TL Characteristics Glow Curve The plot of the thermoluminescence intensity (I) as a function of sample temperature achieved during read out Glow curve may be consisting of one or more peaks May or may not be resolved [1] Reproducibility The measure of the extent to which independent results obtained with the same experimental parameters and material but with different conditions of apparatus, laboratories, intervals of time and operator varies [2] [1]. C. Furetta , “Handbook of Thermoluminescence”, 2 nd Ed., World Scientific Publishing Co. Inc., USA, (2003) [2]. A. D. McNaught and A. Wilkinson, “IUPAC. Compendium of Chemical Terminology”, 2nd ed. (the "Gold Book”), Blackwell Scientific Publications, Oxford, (1997) 8/8/2011 5

TL Characteristics (cont.): 

TL Characteristics (cont.) Dose Rate Response The variations in the TL intensity of the material with respect to dose rate [1] Fading The spontaneous escape of the charge carriers from the traps with ambient temperature, light or any other means [3] Dose response The plot of the thermoluminescent intensity or response verses absorbed dose [1] [1]. C. Furetta , “Handbook of Thermoluminescence”, 2 nd Ed., World Scientific Publishing Co. Inc., USA, (2003) [3]. S. W. S. Mckeever , “Thermoluminescence of solids”, Cambridge University Press, NK, (1983) 8/8/2011 6

TL Characteristics (Cont.): 

TL Characteristics (Cont.) Energy Response The relative TL response due to incoming radiation of specific energy to that of Co-60 radiations [3] Sensitivity The TL response per unit absorbed dose per unit mass of the TL material [4] [ 3]. S. W. S. Mckeever , “Thermoluminescence of solids”, Cambridge University Press, NK, (1983) [4]. E. Pekpak , A. Yilmaz and G. Ozbayoglu , “An Overview on Preparation and TL Characterization of Lithium Borates for Dosimetric Use”, The Open Min. Proc. J., Vol. 3, (2010), pp 14-24 8/8/2011 7

Materials with TL Characteristics: 

Materials with TL Characteristics various materials were reported to have TL characteristics Natural Quartz, China Clay, topaz, Calcite, Gypsum, Fluorite, Corundum and Apatite [4] Synthetic LiF:Mg,Ti (TLD-100), LiF:Mg,Cu,P (TLD-100H), CaSO 4 :Dy, CaSO 4 :Mn, CaF 2 :Dy and Li 2 B 4 O 7 :Mn [3] 8/8/2011 8 [3]. S. W. S. Mckeever , “Thermoluminescence of solids”, Cambridge University Press, NK, (1983) [4]. M. J. Duchesne, F. Moore, B. F. Long and J. Labrie , “A Rapid Method for Converting Medical Computed Tomography Scanner Topogram Attenuation scale to Hounsfield Unit scale and to obtain Relative Density values”, Engineering Geology, vol. 103, pp-100-105, 2009.

TL Materials as radiation Dosimeter: 

TL Materials as radiation Dosimeter The storage capacity of a TL material Proportionality of TL Intensity to amount of absorbed energy Its reusability makes it suitable for dosimetric applications [2] Various different TL dosimeters were developed [2]. A. J. J. Bos , “Theory of thermoluminescence”, Radiation Measurements, 41, (2007), S45–S56 8/8/2011 9

Properties of TL detectors: 

Properties of TL detectors According to Furetta (2003) the properties desired for a good TL dosimeter are: [1] Good TL sensitivity in Dose ranges of 0.1mGy-100Gy Possibility to manufacture small and easy to use Dosimeter Mechanical stability under ambient conditions Low cost Known energy dependency Independence of response to dosimeter orientation No or very small fading [1]. C. Furetta , “Handbook of Thermoluminescence”, 2 nd Ed., World Scientific Publishing Co. Inc., USA, (2003) 8/8/2011 10

Examples of TL Dosimeters: 

Examples of TL Dosimeters Following are some of the commercially available TL dosimeters [2,3] LiF:Mg,Ti (TLD-100) CaF2:Dy (TLD-200) CaSO4:Dy C (diamond) BeO (most efficient) 7LiF:Mg,T (TLD-700) Having good TL properties makes TLD-100 one of most widely used TL Dosimeter [3]. S. W. S. Mckeever , “Thermoluminescence of solids”, Cambridge University Press, NK, (1983) [2]. A. J. J. Bos , “Theory of thermoluminescence”, Radiation Measurements, 41, (2007), S45–S56 8/8/2011 11

TLD-100: 

TLD-100 Most widely used TL dosimeter Effective Z = 8.14, close to soft tissue (7.4) [5] low fading resistant to corrosion and wear, barely soluble in water and chemically stable material However there exist certain complication [6] Complex Glow curve Non-linear at high doses Efficiency Sensitivity 8/8/2011 12 [5]. M. Moscovitch and Y.S. Horowitz, “Thermoluminescent materials for medical applications: LiF:Mg,Ti and LiF:Mg,Cu,P ”, Radiation Measurements, vol. 41, pp- S71–S77, 2007. [6]. J. Azorin , F. Sepulveda, P. Gonzalez, T. Rivera, C. Furetta and B. S. Basurto , “A Comparison between two LiF:Mg,Cu,P Preparations for Clinical Applications”, CIDES, 2002

TopaZ as TLD: 

TopaZ as TLD Topaz is a commonly known gem stone with composition Al 2 (SiO 4 )(F,OH) 2 Having orthorhombic structure Favorable and competent TL properties Mechanical stability Natural occurrence Hardness 8 ( Mohs Scale ) Effective Z of 11.29 [4] Different researchers (Moss and Mcklveen , Lima et al and Souza et al ) studied topaz [8, 9, 7] Concluded suitability of Topaz as TLD [4]. M. J. Duchesne, F. Moore, B. F. Long and J. Labrie , “A Rapid Method for Converting Medical Computed Tomography Scanner Topogram Attenuation scale to Hounsfield Unit scale and to obtain Relative Density values”, Engineering Geology, vol. 103, pp-100-105, 2009. [7]. D.N. Souza, M.E.G. Valerio , J.F. Lima, “Evaluation of Doses in Radiotherapy using Solid-State Composites based on Natural Colorless Topaz”, Appl. Radiat.and Isot ., 58, (2003), 489-494 [8]. A.L. Moss and J. W. Mcklveen , “Thermoluminescent Properties of Topaz”, Health Phys., 34, (1978), 137-140 [9]. C. A. F. Lima, L. A. R. Rosa and P. G. Chuna , ” The Thermo-luminescence Properties of Brazilian Topaz”, Appl. Radiat . and Isot ., 37, (1986), 135-137 8/8/2011 13

Mohs scale: 

Mohs scale 8/8/2011 14 Mohs Number Material/Mineral 1 (softest) Talc 2 Gypsum 3 Calcite 4 Fluorite 5 Apatite 6 Orthoclase 7 Quartz 8 Topaz 9 Corundum 10 (hardest) Diamond Mohs scale data obtained from “Guide to Field Geology” by Mathur , 2004 S. M. Mathur , “Guide to Field Geology”, Prentice-Hall Pvt. Ltd., India, 2004

Motivation: 

Motivation Limited literature on TL characteristics of Topaz Origin dependent TL behavior of topaz [10] Local existence of topaz (low cost) No detailed published data about comparison of all the TL characteristics of topaz with TLD-100 8/8/2011 15 [10]. D. N. Souza, J. F. Lima and M. E. G. Valerio , “Thermoluminescence of Brazilian Topaz”, Rad. Eff. and Def. in Sol., vol. 135, pp-109-113, 1995

Aims and objectives: 

Aims and objectives The aims and objectives of the present study are; To study various TL characteristics of Topaz and TLD-100 Compare them for both the samples To find out the superior sample in case of each and every characteristics To find out the better choice for TL dosimetry To study and compare their applicability to radiotherapy beams 8/8/2011 16

Materials and Methods: 

Materials and Methods Sample Collection The samples used in the present study are; Commercially available TLD-100 ( Harshaw chemical co.) Chip size of ~ 3.2mm*3.2mm*0.9mm Masses in rang 21.2-25mg Topaz crystals were obtained from a mine near Skardu , Gilgit-Baltistan province Pakistan With a crystal size ranging from 1.5-3.5 cm 8/8/2011 17

Material s and Methods (cont.): 

Material s and Methods (cont.) Sample Preparation TLD-100 chips were used as received Topaz crystals were first cleaned With a procedure adopted by Lima et al and Sardar and Tufail [9, 11] A solution consist of 50% water and 50% Aqua Regia (3HCl+HNO 3 ) to remove dust or any other impurity Large sized Topaz chips were then cut to chips Size 3.2mm*3.2mm*0.9mm As previously studied [8, 11] Using Accutom Precision cut-off machine (Model: Accutom-50, Stucers ) having position accuracy of 5µm These chips were then washed with Acetone to remove any dust or impurity associated with cutting [8]. A.L. Moss and J. W. Mcklveen , “Thermoluminescent Properties of Topaz”, Health Phys., 34, (1978), 137-140 [9]. C. A. F. Lima, L. A. R. Rosa and P. G. Chuna , ” The Thermo-luminescence Properties of Brazilian Topaz”, Appl. Radiat . and Isot ., 37, (1986), 135-137 [11]. M. Sardar and M. Tufail , “Thermoluminescent Characteristics of Topaz from Sabser mine near Sakardu in Northern Pakistan”, Nucl . Inst. And Meth. In Phy . Research B, 269, (2011), 284-287 8/8/2011 18

Material s and Methods (cont.): 

Material s and Methods (cont.) Experimental Procedures Weighing Both the samples were weighed While using digital balance (Model: Chyo JK-200, YMC Co. Ltd, Japan) installed at Environmental monitoring laboratory, Pakistan Institute of Engineering and Applied Sciences (PIEAS) Annealing Both the samples TLD-100 and Topaz chips were annealed at 400 o C for 1 hr Using auto control oven (Model: D237.131.0/2) 8/8/2011 19

Experimental Procedures (cont.): 

Experimental Procedures (cont.) Irradiation Irradiation was carried out with Co-60 calibrator (Model: GWGP-80, Nuclear Power Institute of China), Cs-137 calibrator (Model: OB-85, Buchler , Germany) and Linear accelerator (Model: Oncor: Impression, Siemens, Germany) Both the calibrators are installed at Secondary Standard Dosimetry Laboratory (SSDL) located in Pakistan Institute of Nuclear Science and Technology (PINSTECH) however the Linear Accelerator in Nuclear Medicine, Oncology and Radiotherapy Institute (NORI) Islamabad, Pakistan 8/8/2011 20

Experimental procedures (cont.): 

Experimental procedures (cont.) Reading The response was measured while using a TLD reader/ Analyser (Model:RA”94, Poland) installed at Medical Physics Laboratory PIEAS The heating rate used through out the study was 10 o C/s as suggested by Lilley and Taylor [12] and used by Sardar and Tufail [11 ] and Souza et al [13] Sensitivity Factor All the chips were irradiated for the same dose of 1 Gy with post annealing and post irradiation time of 1 hr Response was measured and a sensitivity factor was found out for each chip As suggested by Furetta and carried out by Sabini et al [1, 14] [1]. C. Furetta , “Handbook of Thermoluminescence”, 2 nd Ed., World Scientific Publishing Co. Inc., USA, (2003) [11],M. Sardar and M. Tufail , “Thermoluminescent Characteristics of Topaz from Sabser mine near Sakardu in Northern Pakistan”, Nucl . Inst. And Meth. In Phy . Research B, 269, (2011), 284-287 [12]. G. C. Taylor and E. Lilley, “Rapid readout rate studies of thermoluminescence in LiF (TLD-100) crystals: III.” J. Phys. D: Appl. Phys. 15, (1982), 2053–2065 [13]. K. S. Bomfim and D. N. Souza, “Applicability of Topaz Composites to Electron Dosimetry”, J. Phys.: Conf. Ser., 249, (2010), 012-057 [14]. M.G. Sabini , M. Bucciolini , G. Cuttone , A. Guastie , S. Mazzocchi and L. Raffaele , “TLD-100 Glow-curve Deconvolution for the Evaluation of the Thermal Stress and Radiation Damage Effects ”, Nucl . Instr. and Meth. in Phy . Research A, 476, (2002), 779–784 8/8/2011 21

Experimental procedures (cont.): 

Experimental procedures (cont.) Post Annealing Time 8 hrs for all except sensitivity ~1 hr Post irradiation time For sensitivity ~ 1 hr For reproducibility ~24 hrs For all others ~72 hrs Doses 1cGy – 100Gy for dose response Glow curve only for 6, 10 and 20Gy 1Gy for Reproducibility, Fading, Dose Rate Response, Energy response and sensitivity All the data points produced are based on average of 2-5 chips 8/8/2011 22

Results and discussion : 

Results and discussion [1]. C. Furetta , “Handbook of Thermoluminescence”, 2 nd Ed., World Scientific Publishing Co. Inc., USA, (2003) [9]. C. A. F. Lima, L. A. R. Rosa and P. G. Chuna , ” The Thermo-luminescence Properties of Brazilian Topaz”, Appl. Radiat . and Isot ., 37, (1986), 135-137 [11],M. Sardar and M. Tufail , “Thermoluminescent Characteristics of Topaz from Sabser mine near Sakardu in Northern Pakistan”, Nucl . Inst. And Meth. In Phy . Research B, 269, (2011), 284-287 Sensitivity Three different sensitivity levels observed However Lima et al. observed sensitivity 150 times less than TLD-100 [9] Sardar and Tufail [11] also reported lower sensitivity for topaz variations might be Cleavage cutting Optical density [1] Sample No. of Chips Relative Sensitivity ( w.r.t TLD-100) TLD-100 40 1 Topaz Batch-A 18 0.15 Topaz Batch-B 5 1.76 Topaz Batch-C 6 2.41 8/8/2011 23 data obtained for sensitivity of the samples with irradiation for 1Gy with Co-60, heating rate of 10°C/s and post annealing and post irradiation time of 1hr

Glow curves: 

Glow curves Glow Curve Analysis of TLD-100 annealed at 400­ o C for 1 hr, post annealing time of 8 hrs, Irradiated with Co-60 for 6Gy and a post irradiation time of 72 hrs (β=10 o C/s) Peak # Temprature (present study) Sabini et al. (1 o C/s) [14] YAZICI (2 o C/s) [15] Harvey et al. (10 o C/s) [16] 2 131 114/12.97% 118/9.92% 132/0.76% 3 177 160/9.60% 160/9.60% 170/3.95% 4 189 193/1.04% 190/0.52% 200/4.71% 5 200 220/8.91% 220/8.91% 222/9.90% 7 250 285/9.12% 285/9.12% ---------- 8/8/2011 24 The maximum variation is 12.97 % which might be due to use of different heating rate as reported by Ogundare et al [17] [14]. M.G. Sabini , M. Bucciolini , G. Cuttone , A. Guastie , S. Mazzocchi and L. Raffaele , “TLD-100 Glow-curve Deconvolution for the Evaluation of the Thermal Stress and Radiation Damage Effects ”, Nucl . Instr. and Meth. in Phy . Research A, 476, (2002), 779–784 [15]. A. N. YAZICI, “Defect Structure of Glow Peak 1 in LiF:Mg,Ti (TLD-100)”, Turk J. Phys., 26, (2002) , 473 – 481 [16]. J. A. Harvey, N. P. Haverland and K. J. Kearfott , “Characterization of the Glow-peak Fading Properties of Six Common Thermoluminescent Materials”, Appl. Radiat . and Isot ., 68, (2010), 1988–2000 [17]. F. O. Ogundare , F. A. Balogun and L. A. Hussain , “Heating rate effects on the Thermoluminescence of Fluorite”, Radiation Measurements, 40, (2005), 60–64

Glow Curve (cont.): 

Glow Curve (cont.) Glow Curve Analysis of Topaz Sample annealed at 400 o C, post annealing time of 8 hrs, Irradiated with Co-60 for 6 Gy and with a post irradiation time of 72 hrs (β=10 o C/s) Four peaks at 71 (peak 1) 171 o C (peak 2) 197 o C (peak 3) 250 o C (peak 4) Previously reported peaks Lima et al [9] 100 o C, 130 o C, 200 o C and 250 o C Souza et al [10] 80 o C , 150 o C, 180 o C and 300 o C However Souza et al [10] concluded peak position and No. depends on origin 8/8/2011 25 [9]. C. A. F. Lima, L. A. R. Rosa and P. G. Chuna , ” The Thermo-luminescence Properties of Brazilian Topaz”, Appl. Radiat . and Isot ., 37, (1986), 135-137 [10]. D. N. Souza, J. F. Lima and M. E. G. Valerio , “Thermoluminescence of Brazilian Topaz”, Rad. Eff. and Def. in Sol., 135, (1995), 109-113

Glow Curve (cont.): 

Glow Curve (cont.) A comparison of Glow curve Behavior of TLD-100 and Topaz annealed at 400 o C for 1 hr, post annealing time of 8 hrs, irradiated for 16 Gy with Co-60 and with post irradiation time of 72 hrs (β=10 o C/s) For Topaz more than 60% of TL intensity are at temperature above TLD-100 Peaks Suggests superior stability for topaz at ambient temperature [10] 8/8/2011 26 [ 10]. D.N. Souza, M.E.G. Valerio , J.F. Lima, “Evaluation of Doses in Radiotherapy using Solid-State Composites based on Natural Colorless Topaz”, Appl. Radiat.and Isot ., 58, (2003), 489-494

Glow Curve (Cont.): 

Glow Curve (Cont.) 8/8/2011 27 Dose dependency of glow curve of a) TLD-100 and b) topaz, irradiated for different doses with Co-60, post annealing time of 8hrs, post irradiation time of 72hrs and heating rate of 10°C/s [6]. J. Azorin , F. Sepulveda, P. Gonzalez, T. Rivera, C. Furetta and B. S. Basurto , “A Comparison between two LiF:Mg,Cu,P Preparations for Clinical Applications”, CIDES, 2002 [18]. E. G. Yukihara and E. Okuno , “Non-first-order thermoluminescent peaks in topaz”, Radiation Effects & Defects in Solids, Vol. 146, pp. 277-284, 1998.

Dose dependency of Glow peaks: 

Dose dependency of Glow peaks 8/8/2011 28 the glow peak dose dependency of TLD-100 (left) and topaz (right) irradiated for various doses with Co-60 with post annealing time of 8hrs, post irradiation time of 72 hrs and heating rate of 10°C/s [18]. E. G. Yukihara and E. Okuno , “Non-first-order thermoluminescent peaks in topaz”, Radiation Effects & Defects in Solids, Vol. 146, pp. 277-284, 1998. [19]. M. Moscovitch and Y.S. Horowitz, “Thermoluminescent materials for medical applications: LiF:Mg,Ti and LiF:Mg,Cu,P ”, Radiation Measurements, vol. 41, pp- S71–S77, 2007

Energy dependency of glow curve: 

Energy dependency of glow curve Energy dependency of glow curve behavior of a) TLD-100 and b) topaz, irradiated for a dose of 10Gy, post annealing time of 8hrs, post irradiation time of 72hrs and heating rate of 10°C/s 8/8/2011 29 The energy dependency of TLD-100 is mainly attributed to large grain sizes [3] [3]. S. W. S. Mckeever , “Thermoluminescence of solids”, Cambridge University Press, NK, 1983

Dose rate response: 

Dose rate response A comparative representation of dose rate dependency of TLD-100 and Topaz chips annealed at 400 o C for 1 hr, post annealing time of 8 hrs, irradiated with Co-60 and post irradiation time of 72 hrs (β=10 o C/s) 8/8/2011 30 TLD-100 Maximum of 14 % However STDEV of 5.7% Topaz Maximum in data points 13 % With STDEV of 5.5% [20]. N. Goldstein, “Dose-rate dependence of lithium fluoride for exposures above 15,000 R per pulse”, Health Phys., vol. 22(1), pp-90-91, 1972.

Reproducibility : 

Reproducibility Reproducibility of TLD-100 and Topaz samples annealed for 1 hr at 400 o C, post annealing time of 8 hrs, irradiated for 1 Gy with Co-60 and a post annealing time of 24 hrs (β=10 o C/s) TLD-100 % STDEV Found 4.17% REPORTED By Moor et al 6.7 % [22] Topaz % STDEV 7.19% and Maximum 21.2% Reported Moss and Mcklveen , 20% [8] Sardar and Tufail , 11%[10] 8/8/2011 31 [8]. A.L. Moss and J. W. Mcklveen , “Thermoluminescent Properties of Topaz”, Health Phys., 34, (1978), 137-140 [10]. M. Sardar and M. Tufail , “Thermoluminescent Characteristics of Topaz from Sabser mine near Sakardu in Northern Pakistan”, Nucl . Inst. And Meth. In Phy . Research B, 269, (2011), 284-287 [21]. D. M. Moor, B. Horspool and R. P. Stokes, “Performance of the Harshaw DXT-RAD (TLD-100) Dosimeter”, Radiation Measurements, vol. 43, pp-533–537, 2008 .

fading: 

fading Fading (left) and Percentage Fading (right) of TLD-100 and Topaz Sample annealed at 400 o C, Irradiated with Co-60 for 1Gy and with post annealing time of 8 hrs (β=10 o C/s) TLD-100 Behavior Found Logarithmic Fading Found Rapid 10.67% in first 24 hrs 7.2% in next 19 days Topaz Behavior logarithmic Fading Rapid 8.16% in first 24hrs 16% in next 19days 8/8/2011 32 [8]. A.L. Moss and J. W. Mcklveen , “Thermoluminescent Properties of Topaz”, Health Phys., 34, (1978), 137-140 [10]. M. Sardar and M. Tufail , “Thermoluminescent Characteristics of Topaz from Sabser mine near Sakardu in Northern Pakistan”, Nucl . Inst. And Meth. In Phy . Research B, 269, (2011), 284-287 [22]. A. N. YAZICI, “Defect Structure of Glow Peak 1 in LiF:Mg,Ti (TLD-100)”, Turk J. Phys., 26, (2002) , 473 – 481 [23]. J. A. Harvey, N. P. Haverland and K. J. Kearfott , “Characterization of the Glow-peak Fading Properties of Six Common Thermoluminescent Materials”, Appl. Radiat . and Isot ., 68, (2010), 1988–2000

Energy Response: 

Energy Response TLD-100 Constant for Co-60 & Cs-137 Reduces to 0.93 and 0.87 for 6MV and 15MV respectively Reported, 0.989 and 0.974 for 6MV and 25MV [24] Topaz Nearly constant for Co-60 and Cs-137 (2%) [11] Reduces to 0.93 and 0.94 for 6MV and 15MV 8/8/2011 33 Comparison of Energy dependency of TLD-100 and topaz, irradiated for 10Gy, post annealing and post irradiation time of 8hrs and 72hrs respectively and heating rate of 10°C/s [11]. M. Sardar and M. Tufail , “Thermoluminescent Characteristics of Topaz from Sabser mine near Sakardu in Northern Pakistan”, Nucl . Inst. And Meth. In Phy . Research B, 269, (2011), 284-287 [24]. P. N. Mobit , P. Mayles and A. E. Nahum, “The quality dependence of LiF TLD in megavoltage photon beams: Monte Carlo simulation and experiments”, Phys. Med. Biol., vol. 41, pp-387-398, 1996

Dose Response: 

Dose Response TLD-100 Linear up to 4Gy (R 2 =0.98) Quadratic above 4Gy (R 2 =0.99) Topaz Linear up to 20Gy (R 2 =0.97) Quadratic above 20Gy (R 2 =0.99) 8/8/2011 34 Comparison of dose response TLD-100 (left) and topaz (right), irradiated with Co-60, post annealing and post irradiation time of 8hrs and 72hrs respectively and heating rate of 10°C/s Reported TLD-100 Linear up to 4Gy and nonlinear above 4Gy [25] Topaz Linear up to 20Gy and Nonlinear above [26]

Applicability to clinical radiotherapy (dose linearity): 

Applicability to clinical radiotherapy (dose linearity) TLD-100 Linear for all three beam energies Topaz Linear for all However the slope For 15MV is greater Might be due to neutron sensitivity [27] As evident in TLD-100 [28] 8/8/2011 35 Comparative study of the linearity of TLD-100 (left) and topaz (right) irradiated for doses 1-4Gy with different radiotherapeutic beams, post annealing and post irradiation time of 8hrs and 72hrs respectively and heating rate of 10°C/s [27]. A. Alfuraih , M. P. W. Chin and N. M. Spyrou , ”Measurements of the Photonuclear Neutron yield of 15 MV Medical Linear Accelerator”, Journal of Radioanalytical and Nuclear Chemistry, vol. 278 (3), pp-681–684, 2008. [28]. S. Miljanić , K. Krpan and S. Blagus , “TL and PTTL of TLD-100 and TLD-700 after Irradiation with 14.5MeV Neutrons”, Nucl . Inst. and Meth. in Phy . Res. A, vol. 574, pp-510–517, 2007.

Dose pRofile: 

Dose pRofile Although Results are not convincing as for as Dose profile is concerned (might be due to detector geometry ) But the comparative results shows that topaz shows comparable results to that of TLD-100 8/8/2011 36 Comparison of dose profile obtained with TLD-100 and topaz for a) 6MV and b) 15MV irradiated for 1Gy, post annealing and post irradiation time of 8hrs and 72hrs respectively and heating rate of 10°C/s

conclusions: 

conclusions Following are the main concluded points Topaz sample studied showed variable sensitivity in some cases more than TLD-100 The glow peaks of Topaz occurs at higher temperatures as compared to TLD-100 Which demands greater stability for Topaz at ambient temperature The dose rate dependency of Topaz is smaller than TLD-100 and is less then 10% Fading for Topaz is relatively greater then that of TLD-100 Both the samples show energy dependency in megavoltage ranges Reproducibility of Topaz is found to comparable to that of TLD-100 Linearity range of topaz is up to higher Doses than TLD-100 The topaz shows linearity for the three common energies used in radiotherapy The above conclusion makes Topaz a competitive material to be used as TL dosimeter 8/8/2011 37

Future recommendations : 

Future recommendations Detailed study of topaz in radiotherapy Might be used for Depth doses, entrance and exit doses, scatter doses and QA Study regarding TL characteristics of topaz At low energy x-rays 30keV-150keV used in diagnostic radiology for mixed radiations 8/8/2011 38

References : 

References C. Furetta , “Handbook of Thermoluminescence”, 2 nd Ed., World Scientific Publishing Co. Inc., USA, (2003) A. J. J. Bos , “Theory of thermoluminescence”, Radiation Measurements, 41, (2007), S45–S56 S. W. S. Mckeever , “Thermoluminescence of solids”, Cambridge University Press, NK, (1983) M. J. Duchesne, F. Moore, B. F. Long and J. Labrie , “A Rapid Method for Converting Medical Computed Tomography Scanner Topogram Attenuation scale to Hounsfield Unit scale and to obtain Relative Density values”, Engineering Geology, vol. 103, pp-100-105, 2009. M. Moscovitch and Y.S. Horowitz, “Thermoluminescent materials for medical applications: LiF:Mg,Ti and LiF:Mg,Cu,P ”, Radiation Measurements, vol. 41, pp- S71–S77, 2007. J. Azorin , F. Sepulveda, P. Gonzalez, T. Rivera, C. Furetta and B. S. Basurto , “A Comparison between two LiF:Mg,Cu,P Preparations for Clinical Applications”, CIDES, 2002 D.N. Souza, M.E.G. Valerio , J.F. Lima, “Evaluation of Doses in Radiotherapy using Solid-State Composites based on Natural Colorless Topaz”, Appl. Radiat.and Isot ., 58, (2003), 489-494 A.L. Moss and J. W. Mcklveen , “Thermoluminescent Properties of Topaz”, Health Phys., 34, (1978), 137-140 C. A. F. Lima, L. A. R. Rosa and P. G. Chuna , ” The Thermo-luminescence Properties of Brazilian Topaz”, Appl. Radiat . and Isot ., 37, (1986), 135-137 D. N. Souza, J. F. Lima and M. E. G. Valerio , “Thermoluminescence of Brazilian Topaz”, Rad. Eff. and Def. in Sol., vol. 135, pp-109-113, 1995 M. Sardar and M. Tufail , “Thermoluminescent Characteristics of Topaz from Sabser mine near Sakardu in Northern Pakistan”, Nucl . Inst. And Meth. In Phy . Research B, 269, (2011), 284-287 G. C. Taylor and E. Lilley, “Rapid readout rate studies of thermoluminescence in LiF (TLD-100) crystals: III.” J. Phys. D: Appl. Phys. 15, (1982), 2053–2065 K. S. Bomfim and D. N. Souza, “Applicability of Topaz Composites to Electron Dosimetry”, J. Phys.: Conf. Ser., 249, (2010), 012-057 8/8/2011 39

References (cont.): 

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